DHA is contained in oil from fish belonging to the group of blue fish. Particularly, DHA is contained in the oil from sardines or tuna, in which DHA is contained in an amount of around 20%.
Recently, due to the discovery of fish material containing a high concentration of DHA such as the orbital fat of tuna, or due to the progress in technology for producing highly purified fatty acids, intensive efforts have been made to elucidate the physiological functions of DHA, and to investigate its practical use. It has become apparent that the physiological functions of DHA include an effect of lowering cholesterol, an anticoagulant effect and a carcinostatic effect. In relation to the metabolic system of brain, it has also become apparent that DHA is effective in improving memory and learning, preventing senile dementia, and treating Alzheimer's disease. In addition, it has been proved that DHA is an essential fatty acid for the growth of fry. For the reasons mentioned above, DHA is used in various foods, feedstuffs and baits.
DPA is also known to be contained in fish oil, although the content is extremely low. Most of the physiological functions of DPA are still unknown. The only function known for DPA is its usefulness as a carrier for transporting pharmaceutical agents into brain [Japanese Patent Publication (Kokai) No. 61-204136 (1986)]. It is expected, however, that DPA may play a physiological role in the animal body, since it is known that DPA increases in compensation for a lack of DHA in an animal body [Homayoun et al., J. Neurochem., 51:45 (1988); Hamm et al., Biochem. J., 245:907 (1987); and Rebhung et al., Biosci. Biotech. Biochem., 58:314 (1994)].
If one intends to obtain DHA and/or DPA from fish oil, several disadvantages exist, for example, the low content of the desired fatty acids, the inability to maintain a stable source of fish oil due to the migration of fish, or the offensive odor inherent in fish oil. In addition, it is difficult to obtain lipids with reliable quality, since fish oil additionally contains unsaturated fatty acids such as arachidonic acid (ARA) and eicosapentaenoic acid (EPA), which makes the lipids susceptible to oxidization.
Besides fish oil, lipids accumulated in cultured cells of a microorganism having an ability to produce DHA and/or DPA is considered as a source of DHA and/or DPA. For example, the following microorganisms are known to produce DHA and/or DPA: Vibrio marinus ATCC 15381, a bacterium isolated from the deep sea; Vibrio bacteria Isolated from an intestines of a deep sea fish; flagellate fungi such as Thraustochytrium aureum ATCC 34304, Thraustochytrium sp. ATCC 28211, ATCC 20890 and ATCC 20891, Schizochytrium sp. ATCC 20888 and ATCC 20889 (U.S. Pat. No. 5,340,742), Thraustochytrium SR21 strain (Nippon Nogei Kagaku Kaishi, vol. 69, extra edition. Jul. 5, 1995), and Japonochytrium sp. ATCC 28207 [Japanese Patent Publication (Kokai) No. 1-199588 (1989)]; micro-algae such as Cyclotella cryptica, Crypthecodinium cohnii [Japanese Patent Publication (Kohyo) No. 5-503425 (1993)], and Emiliania sp. [Japanese Patent Publication (Kokai) No. 5-308978 (1993)].
In using any of the above-mentioned microorganisms, however, several problems exist, for example, a low yield of DHA and/or DPA, a requirement of a prolonged culture period for obtaining a sufficient amount of DHA and/or DPA, or a requirement of a specific medium or culture condition for production. When an alga such as Emiliania sp. is utilized for the production, a high yield of DHA may be accomplished, although there may exist a disadvantage that the culture steps are complicated due to the requirement of light for cultivation. Consequently, such a process is not suitable for industrial production.
Thus, the present invention described herein makes possible the advantage of providing a process which can produce DHA and/or DPA as well as lipids containing DHA and/or DPA using an inexpensive and conventional medium and simple steps for production, in a short period and in a high yield.
The present invention provides a process for preparing lipids containing DHA and/or DPA comprising cultivating in a medium a microorganism belonging to the genus Ulkenia having the ability to produce DHA and/or DPA, and recovering the lipids from the culture.
The present invention also provides a process for preparing DHA and/or DPA comprising cultivating in a medium a microorganism belonging to the genus Ulkenia having the ability to produce DHA and/or DPA, recovering the lipids from the culture, and separating the DHA and/or DPA from the lipids.